Dennis C. Evans p1 SuperNova/Acceleration Probe 16 November 2001 Optical Analysis & Stray Light...

16 November 2001

Optical Analysis & Stray Light Evaluation Dennis C. Evans p1

SuperNova/Acceleration Probe

Optical Analysisand

Stray Light Evaluation

Dennis Charles Evans

16 November 2001

16 November 2001



• ZEMAX Optical Layout ISAL prescription from TMA62 write-up Checked against customer supplied

ZEMAX

• Optical Sensitivities Basic Sensitivity Active Secondary (5-dof)

• Stray Light Baffle Layout• Spectrograph Enclosure and Insertion• Views from the Detector• Solar Flux• Open Items

16 November 2001



• ZEMAX Optical Layout ISAL prescription from TMA62 write-up Checked against customer supplied

ZEMAX

16 November 2001



16 November 2001



Optical Sensitivity•Basic Sensitivity

Individual Element Increments of 0.001 mm or degree to 0.016

MF Limit (RMS Spot Radius)(0.002837÷0.005000)*2 = 0.32194276

•Active Secondary Five degree-of-freedom

—Dx, Dy, Dz, Tx, Ty Limits on Secondary

— ± 1 mm or degree Limits on Elements

— ± 0.256 mm or degree

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Basic Limit Active Secondary Limit

Primary Tilt 0.0003 deg 0.185 deg

Primary-Secondary

Space

0.0008 mm 0.033 mm

Tertiary Tilt 0.016 deg 0.055 deg

Key Tolerance Comparison

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• Basic Sensitivity (limited to 0.005 RMS Radius)TETX TETY Tilt about X & Y 5=Primary 0.000335 deg ×3600 arc-sec/deg = 1.206 arc-secTTHI Thickness 4-6; 0.000802 mm TRAD Radius of Curvature 5 0.001604 mm (= same effect as thickness change)TIRX TIRY Sag (Tilt) Across Lens 5 0.011705 mmTSDX TSDY Surface Decenter 5 0.014518 mmTEDX TEDY Element Decenter 5 0.014518 mm

TETX TETY Tilt about X & Y 8=Secondary 0.001515 deg ×3600 arc-sec/deg = 5.454 arc-secTTHI Thickness 7-9; 0.000602 mm TRAD Radius of Curvature 8 0.001828 mm TIRX TIRY Sag (Tilt) Across Lens 8 0.011261 mmTSDX TSDY Surface Decenter 8 0.014658 mmTEDX TEDY Element Decenter 8 0.014658 mm

TETX Tilt about X & Y 17=Fold Flat 0.008217 deg ×3600 arc-sec/deg = 5.454 arc-secTETY Tilt about X & Y 17 0.011621 deg ×3600 arc-sec/deg = 5.454 arc-secTTHI Thickness 16-18; 0.018010 mm TRAD Radius of Curvature 17 insensitive at 0.256 change TIRX Sag (Tilt) Across Lens 17 0.150454 mm TIRY Sag (Tilt) Across Lens 17 0.106387 mmTSDX TSDY Surface Decenter 17 insensitive at 0.256 change (0.002884)TEDX TEDY Element Decenter 17 insensitive at 0.256 change (0.002884)

TETX TETY Tilt about X & Y 22=Tertiary 0.016927 deg ×3600 arc-sec/deg = 60.9372 arc-secTTHI Thickness 21-23; 0.016919 mm TRAD Radius of Curvature 22 0.031079 mm TIRX TIRY Sag (Tilt) Across Lens 22 0.199252 mmTSDX TSDY Surface Decenter 22 insensitive at 0.256 change (0.003732)TEDX TEDY Element Decenter 22 insensitive at 0.256 change (0.003732)

TETX TETY Tilt about X & Y 32-33=Filter insensitive at 0.256 change (0.002886)TTHI Thickness 21-23; 0.016919 mm TRAD Radius of Curvature 22 0.031079 mm TIRX TIRY Sag (Tilt) Across Lens 22 0.199252 mmTSDX TSDY Surface Decenter 22 insensitive at 0.256 change (0.003732)TEDX TEDY Element Decenter 22 insensitive at 0.256 change (0.003732)

TTHI Filter to Image 36-37 0.136618 mm (Image Plane is compensator for fast analysis)

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|------------ Minimum ------------| |------------ Maximum ------------|Type Value MF Change Value MF Change(Primary Mirror)Thickness tolerance on surface 4 TTHI 4 6 -0.033610 0.005000 0.002163 0.033112 0.005000 0.002163 Thickness 8: 1.00001E+000 -1.00001E+000Radius tolerance on surface 5TRAD 5 -0.066773 0.004566 0.001730 0.066242 0.005000 0.002163 Thickness 8: 1.00001E+000 -1.00001E+000Tilt X tolerance on surfaces 5 through 5 (degrees)TETX 5 5 -0.185670 0.005000 0.002163 0.185670 0.005000 0.002163 Parameter 2 on Surface 7: 9.12416E-002 -9.12419E-002 Parameter 3 on Surface 7: -1.87703E-001 1.87703E-001Tilt Y tolerance on surfaces 5 through 5 (degrees)TETY 5 5 -0.185720 0.005000 0.002163 0.185720 0.005000 0.002163 Parameter 1 on Surface 7: -9.12903E-002 9.12680E-002 Parameter 4 on Surface 7: -1.87754E-001 1.87754E-001

(Fold Flat)Thickness tolerance on surface 16TTHI 16 18 -0.256000 0.004764 0.001927 0.256000 0.004764 0.001927 Thickness 8: 1.74322E-001 -1.87717E-001TIRX 17 -0.256000 0.004388 0.001551 0.256000 0.004388 0.001551 Parameter 1 on Surface 7: -5.13796E-001 5.13786E-001TIR Y tolerance on surface 17TIRY 17 -0.222637 0.005000 0.002163 0.222637 0.005000 0.002163 Parameter 2 on Surface 7: 6.31916E-001 -6.31897E-001Tilt X tolerance on surfaces 17 through 17 (degrees)TETX 17 17 -0.017196 0.005000 0.002163 0.017196 0.005000 0.002163 Parameter 2 on Surface 7: 6.31902E-001 -6.31891E-001Tilt Y tolerance on surfaces 17 through 17 (degrees)TETY 17 17 -0.024319 0.005000 0.002163 0.024319 0.005000 0.002163

(Tertiary Mirror)Tilt X tolerance on surfaces 22 through 22 (degrees)TETX 22 22 -0.055298 0.005000 0.002163 0.055298 0.005000 0.002163 Parameter 2 on Surface 7: -1.00001E+000 1.00001E+000Tilt Y tolerance on surfaces 22 through 22 (degrees)TETY 22 22 -0.055298 0.005000 0.002163 0.055298 0.005000 0.002163 Parameter 1 on Surface 7: 1.00001E+000 -1.00001E+000

Active Secondary Sensitivity

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•Stray Light Baffle Layout

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16 November 2001



• Spectrograph Enclosure and Insertion

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16 November 2001



• Views from the Detector

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16 November 2001



• Solar Flux Concentrations inside Instrument Solar Flux = 1 SC = .1367 watt.cm-2 = 1367 watt.m-2

Location Image Radius (mm)

Flux (SC)

Flux(watt.cm-

2)

Flux(watts

)

Entrance Aperture 1000 1 .1367 4295

Secondary Mirror 213 22 3.1 4295

Prime Focus Ring 10.7 4367 597 2147

Focal Plane 1 64 244 33 4295

Shutter Pupil 48 437 60 4295

FP 2 (CCD/Image) 96 109 15 4295

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Open Items&

Concerns

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• Open Items

Shade angle (<30o?) and Barrel Baffle length Baffle edge finish (Forward Ring) Cleanliness, especially of Primary Mirror Aft Optics Baffles (Mostly black paint) MLI outer layer vs. mission length Reverse views

— AutoCAD Photo Ray Trace— reverse ray trace, TMA62

Focal plane — parfocalization (filter thickness)

S/G placement — behind focal plane?— center mounted

ASAP diffuse scatter model — (Friday PM – Next Week)

16 November 2001



• Mission Unique Concerns: No mission unique concerns have been

observed.

Stray light issues are manageable using proven baffling techniques that have been successfully demonstrated on flight missions.

Analysis done too early in the design cycle is likely to give false confidence (analytical design is better than real design).

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• Central Obscuration Minimum possible - about 5% (Shadow of

Secondary)

Current minimum design to keep direct light from Focal Surface 1 - about 15%

Maximum practical limit to keep direct light from inner baffle interior and front lip - slightly less than 25%

16 November 2001



• Stray Light Issues Similarity to flight instruments shows successful design is possible

—HST, FUSE, COBE-DIRBE, IUE, OAO

Similarity to flight instruments shows design flaws are possible that will not be detected by stray light analysis, but by careful design, inspection, and testing.

—HST - Door reflections—DIRBE - Barrel Baffle side wall single bounces.—IUE/OAO - Pinhole leaks into aft optics assemblies; bolt head locations.

Design & Analysis Similarity—SIRTF - IRAC—WIRE (minor changes make orders of magnitude stray light differences)—GOES Earth Limb Sensor (light leaks around filters and side wall reflections)—MODIS - Stray light in calibrator designs, not instrument designs

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• Focus Drive Mechanism Definition of acceptable image size needs to be

reviewed. RMS radius of 0.005 mm may be to conservative for

a pixel limited performance instrument. Range of motions used were +/- 1 mm and degree. The Displacement motions may be effectively

increased to 5 or 10 mm for some corrections. Tolerance analysis so far is only with two elements at

a time and has not included Image Plane tilts.

16 November 2001



• View from the detector inspection is important. Fold Flat throat can be illuminated by sky. Fold flat throat design as in this study may not

allow AFT star tracker

• AFT optics baffles and black surfaces Baffles not designed yet Black paint has been known to cause CTE

changes in GFRP structures.

Dennis C. Evans p1 SuperNova/Acceleration Probe 16 November 2001 Optical Analysis & Stray Light...

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